This invention relates generally to apparatus and method for controlling the flow of various fluids, such as water, petroleum liquids and the like. One type of sealing means now being used in various types of flow control apparatus, such as valves, flow diverters and meter provers employs a plunger having sealing cups made of resilient material. The plunger assembly is arranged to move into and out of a cylindrical sleeve to arrest or permit flow of liquid though the same. In U.S. Pat. No. 3,827,285 granted Aug. 6, 1974, apparatus of this type makes use of two cups which have their rims faced away from each other. When such an arrangement is used to control flow of fluid through the sleeve, contraction of the rims of the cups as the plunger assembly is moved into the sleeve causes a pressure drop to be induced in the closed space between the cups, and the maintenance of this self-induced pressure drop is used to detect any leakage. Such flow control apparatus is being used commercially in meter provers and flow diverters.
Proper sealing of the resilient cups in such apparatus is in part dependent upon the properties of the resilient material from which they are made. In the event there is a tendency for the cups to undergo dimensional changes, as for example, a shrinkage in diameter due to the effect of the liquids involved or changes in elasticity due to aging of the resilient material, the peripheral areas of the cup rims may be urged against the inner cylindrical surface of the sleeve with less force, thus occasioning the risk of leakage, particularly when the self-induced pressure drop is substantial, since it tends to reduce the contact pressure of the rims against the sleeve.